ABSTRACT
A high proportion of disorders affecting the skin and its appendages follow Mendelian inheritance, and because they are readily available for inspection, they are easier than most to document in families. Light-skinned individuals of mixed ancestry married to a ‘white’ person may enquire as to whether a child or subsequent descendant might have extremely dark skin colour or African features — in other words, might be a clearly black person who perhaps would not be accepted in the ‘white’ community into which he or she is born. Several unusual disorders of skin pigmentation have been described that follow a patchy or whorled distribution corresponding to the lines of Blaschko, and which may be accompanied by mental retardation or other systemic features. Basal cell naevus syndrome is a dominantly inherited disorder which may be recognised from skeletal abnormalities, especially jaw cysts, before tumours appear.
